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diff --git a/common/kernel/sso_array.h b/common/kernel/sso_array.h
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+/*
+ *  nextpnr -- Next Generation Place and Route
+ *
+ *  Copyright (C) 2018  Claire Xenia Wolf <claire@yosyshq.com>
+ *  Copyright (C) 2018  Serge Bazanski <q3k@q3k.org>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#ifndef SSO_ARRAY_H
+#define SSO_ARRAY_H
+
+#include <cstdint>
+
+#include "nextpnr_assertions.h"
+#include "nextpnr_namespaces.h"
+
+NEXTPNR_NAMESPACE_BEGIN
+
+// An small size optimised array that is statically allocated when the size is N or less; heap allocated otherwise
+template <typename T, std::size_t N> class SSOArray
+{
+  private:
+    union
+    {
+        T data_static[N];
+        T *data_heap;
+    };
+    std::size_t m_size;
+    inline bool is_heap() const { return (m_size > N); }
+    void alloc()
+    {
+        if (is_heap()) {
+            data_heap = new T[m_size];
+        }
+    }
+
+  public:
+    T *data() { return is_heap() ? data_heap : data_static; }
+    const T *data() const { return is_heap() ? data_heap : data_static; }
+    std::size_t size() const { return m_size; }
+
+    T *begin() { return data(); }
+    T *end() { return data() + m_size; }
+    const T *begin() const { return data(); }
+    const T *end() const { return data() + m_size; }
+
+    SSOArray() : m_size(0){};
+
+    SSOArray(std::size_t size, const T &init = T()) : m_size(size)
+    {
+        alloc();
+        std::fill(begin(), end(), init);
+    }
+
+    SSOArray(const SSOArray &other) : m_size(other.size())
+    {
+        alloc();
+        std::copy(other.begin(), other.end(), begin());
+    }
+
+    SSOArray(SSOArray &&other) : m_size(other.size())
+    {
+        if (is_heap())
+            data_heap = other.data_heap;
+        else
+            std::copy(other.begin(), other.end(), begin());
+        other.m_size = 0;
+    }
+    SSOArray &operator=(const SSOArray &other)
+    {
+        if (&other == this)
+            return *this;
+        if (is_heap())
+            delete[] data_heap;
+        m_size = other.m_size;
+        alloc();
+        std::copy(other.begin(), other.end(), begin());
+        return *this;
+    }
+
+    template <typename Tother> SSOArray(const Tother &other) : m_size(other.size())
+    {
+        alloc();
+        std::copy(other.begin(), other.end(), begin());
+    }
+
+    ~SSOArray()
+    {
+        if (is_heap()) {
+            delete[] data_heap;
+        }
+    }
+
+    bool operator==(const SSOArray &other) const
+    {
+        if (size() != other.size())
+            return false;
+        return std::equal(begin(), end(), other.begin());
+    }
+    bool operator!=(const SSOArray &other) const
+    {
+        if (size() != other.size())
+            return true;
+        return !std::equal(begin(), end(), other.begin());
+    }
+    T &operator[](std::size_t idx)
+    {
+        NPNR_ASSERT(idx < m_size);
+        return data()[idx];
+    }
+    const T &operator[](std::size_t idx) const
+    {
+        NPNR_ASSERT(idx < m_size);
+        return data()[idx];
+    }
+};
+
+NEXTPNR_NAMESPACE_END
+
+#endif